This invention relates to an optical signal changeover device and an optical signal changeover method and, in particular, to the optical signal changeover device and the optical signal changeover method that include a redundant configuration used in the multiple-wavelength optical transmission system
The optical network is fast becoming popular as a means of communication network which allows high-speed and large-capacity data transmission. In the back of such popularization, there is the progress in the field of optical wavelength multiplexing technology. By adopting the optical wavelength multiplexing technology which enables a single line of optical fiber cable to transmit multiple optical signals with different wavelengths respectively, it has become possible to transmit in only one cable several to several thousand times more amount of information as compared to when wavelength multiplexing is not available.
The central core in the configuration of the optical network is the optical signal changeover device. The optical signal changeover device is a kind of node unit connecting a plurality of transmission paths. The device dissolves a plurality of multiple-wavelength optical signals coming in through a plurality of optical transmission paths, one from another by difference of wavelength, conducts changeover of paths so as for these optical signals to be outputted to designated paths in groups of wavelengths or destinations, and multiplex wavelengths of the optical signals again before outputting the signals to the optical transmission paths.
As mentioned above, the bigger the transmission volume of network grows, the more the need for expansion in terms of wide-band and capacity becomes acute in regard to optical transmission paths, node units (those optical signal changeover devices, repeaters, etc. which are installed at each node in the network); and at the same time, this would mean so much greater impact to be caused on the transmission service just in case any serious trouble should occur. Therefore, to ensure the reliability of service even at the time of occurrence of trouble, it has been being exercised that the optical signal changeover device is designed to have a dual configuration with an active system and a stand-by system (a redundant configuration). Such dualization or dual configuration is called as redundant or a redundant configuration.
A conventional optical transmission device with a redundant configuration is exemplified by the ones shown in US2003/0123785 and US2003/0185566. Explanation follows with respect to such an optical transmission device provided with a conventional redundant configuration.
In a conventional optical signal changeover device having a redundant configuration, optical signals inputted are first segmented into two groups by the optical bifurcating unit, viz., 1×2 optical couplers 12-1 to 12-N. The segmented input optical signals are sent to N×M optical switches for the active system and also to N×M optical switches for the stand-by system, and these N×M optical switches for the active system and the stand-by system respectively play the role of changing over the optical paths. The optical signals outputted from the N×M optical switches of the active system and the stand-by system are placed under monitoring as to the state of communication. Such monitoring of communication status helps detect occurrence of any failure. The control unit controls a plurality of 2×1 optical switches to carry out changeover and reinstatement between the optical signals of the active system and the optical signals of the stand-by system. The optical signals outputted from the 2×1 optical switches are sent out multiplexed with other optical signals which are also to be sent out to the same transmission path. The correspondence of respective 2×1 optical switches to the outputted optical signals Out1 to OutM and also to the transmission paths is made in a fixed manner.
As to the optical switches used in the optical signal changeover device, known are those micro-electromechanical systems (MEMS) as shown in US2004/0184718.